1. Field of the Invention
The present invention relates to an image-forming apparatus for forming a toner image on a sheet-like material. More specifically, the invention relates to an image-forming apparatus having a fixing device which fixes the toner image on the sheet-like material and is equipped with a heated roller for fusing the toner image and a pressure roller for pressing the sheet-like material against the heated roller.
2. Description of the Related Art
A heated roller type fixing device has been widely applied to electro-photographic image-forming devices in recent years because it has the feature of ensuring stable image fixing in spite of being small in construction.
The heated roller type fixing device is equipped with a heated roller and a pressure roller, and fixes a toner image on a paper sheet by heating and fusing when the paper sheet passes between the heated roller and the pressure roller. Furthermore, the heated roller is capable of housing a heating lamp as a heat source, and the roller surface is coated with a material that is easily separated from the toner image. Heated roller type fixing devices require a long service life for the heated roller.
As one structure proposed to meet this requirement, a heated roller which has a fluorine resin layer on the surface is disclosed in Japanese Patent Publication (Koukoku) No. 3-14350. The fluorine resin layer is formed from a tube made from a copolymer of perfluoroalkyl perfluorovinyl ether. After the tube is applied around the outer surface of the metallic cylinder which is coated with a bonding agent, the fluorine resin is thermally shrunk at a high temperature, to produce the fluorine resin layer.
However, the heated roller having the fluorine resin layer is not commercially acceptable in relation to the fixing performance.